1. Field of the Invention
This invention is directed to artificial prosthetic components and assembly methods therefor for use in a human lower limb prosthesis. More particularly, this invention is directed to improved human prostheses and methods therefor wherein the prosthesis comprises modular prefabricated components.
2. Description of Related Art
The most common artificial leg for below knee amputees is of a rigid nature. A solid shank connects the socket, which mounts the artificial leg to the residual limb of the amputee, and the artificial foot. The shank is often made out of a rigid alloy, such as one containing titanium, or from shaped wood or plastic. It can be solid for strength, or it can be hollow for lightness.
In a typical conventional prosthesis fabrication technique, a significant amount of time and effort is wasted in duplicating fabrication steps. Generally, conventional fabrication includes taking a cast of the patient""s stump and making a socket incorporating the necessary fittings, including (a) an alignment fitting for angular adjustments; (b) a tubular fitting for length and rotational adjustment; (c) a fitting for linear adjustments; and (d) an ankle fitting for angular adjustments and to allow attachment of a foot. The prosthesis is assembled for bench alignment and the patient is scheduled for dynamic alignment. When the patient and prosthesis are satisfied with both the fit of the socket and the alignment of the prosthesis, the prosthesis is duplicated in an alignment device that captures the prosthetic alignment and allows removal of the metal components and replacing them with polyurethane. The area between the top of the keel and the bottom of the socket is foamed in place, and when the foam hardens, the shank is hand shaped to the desired configuration between the keel and the socket. The prosthesis is prepared for the final draping of copolymer plastic. If the finished prosthesis is not satisfactory and can not be adjusted, the process is repeated using the same components. The approximate fabrication time for this procedure is 5 to 8 hours.
As an example, U.S. Pat. No. 4,314,398 discloses a method of making a lower leg prosthesis comprising the steps of (a) forming a temporary prosthesis socket having an inner shape corresponding to the remaining lower leg stump of the amputee to which the prosthesis is to be attached; (b) forming a test prosthesis by fixing an adjustable position testing device to the temporary socket and connecting the testing device to the prosthesis foot through a temporary connecting member; (c) testing the test prosthesis on the patient and adjusting the testing device so as to obtain a proper alignment of the temporary socket in relation to the prosthesis foot; (d) providing a positive prosthesis socket in the temporary socket of the test prosthesis and reproducibly fixing the assembly comprised of the positive socket, the temporary socket, the testing device and at least the temporary connecting member in a support device; (e) removing the test prosthesis parts from the support device; (f) placing the connecting member adjacent the positive socket in the support device in the aligned relative position reproducibly set in the support device in step (d); and (g) forming the prosthesis socket on the positive socket while simultaneously securing the connecting member to the prosthesis socket in the aligned relationship thereby obtaining an individually aligned lower leg prosthesis. However, the method associated with this reference requires duplicating assembly steps; i.e., fixing the adjustable position testing device to a temporary socket and temporarily connecting this device to the prosthesis foot, followed by removing the test prosthesis and replacing it with a permanent member in the position formerly occupied by the testing device.
U.S. Pat. No. 5,152,800 discloses a below the knee prosthesis and method for making the same. The prosthesis includes a socket for receiving the stump of the below-the-knee amputee, a keel having a peripheral groove formed about the periphery of a bottom portion of the keel, a tubular shin member extending from the socket and surrounding lateral and medial portions of the keel and filling the peripheral grooves formed about the bottom portion of the keel leaving a substantial portion of the bottom of the keel exposed. A resilient foot member is then secured to the exposed portion of the keel with the material of the tubular shin member being formed into the grooves of the keel and maintaining such keel within the shin member. The method thereof includes the steps of forming a socket for receiving a stump of the below-the-knee amputee; constructing a shin support about the socket including an ankle block and keel about the socket in accordance with the size and stature of the amputee; forming a retaining means in a bottom surface of the keel for retaining the keel in a predetermined position with respect to the socket; molding a sheet of copolymer material about the shin support, into the retaining means and over the bottom surface of the keel to form a shin member; removing the copolymer material from the bottom surface of the keel; removing a substantial portion of material used to construct the shin support from within the shin member; and securing a foot member to the keel. The method for assembly of this device does not take advantage of a prefabricated socket adapter/pylon/keel assembly, instead requiring several distinct steps for assembling the prosthesis including assembling a shin support between the socket adapter and the keel, foaming the support, draping a copolymer exterior on the assembly, and drilling out the foam shin support.
The prior art also includes continuous one-piece prostheses, such as that shown in U.S. Pat. No. 5,219,364. That prosthesis offers the advantages of light weight and improved energy storage and release characteristics. Because of its design, however, this prosthesis can require multiple patient trips to the prosthetist for fitting. In certain cases the patient may have to be fitted with another prosthesis which will be adjusted for various parameters, including height, pylon length, inversion, and eversion. Once the prosthesis is adjusted, the measurements from the adjusted prosthesis are then used to form the one-piece prosthesis, following a time consuming process. Further, once the prosthesis is manufactured, adjustments may require reheating and reforming the prosthesis.
U.S. Pat. No. 5,993,487 discloses a prosthetic component for use in a human lower limb prosthesis. The component consists of an preformed integrated pylon-keel or foot component. In practice, the prosthetist would perform a stump measurement on the amputee to determine the overall height of the prosthesis from which the pylon length could be determined, then cut a preformed integrated pylon keel prosthesis to fit the pylon to an adjustable tube clamp, whereby the clamp itself is secured to the socket. Then the prosthetist adjusts the tube clamp for inversion eversion, foot position, and rotation, then the integrated pylon/keel is attached to the tube clamp and the apparatus is covered with plastic. However, this is not a complete prosthesis, but merely the pylon/keel assembly. Further, the invention requires the use of an adjustable tube clamp attached to the socket. This additional component adds complexity and weight to the structure. Moreover, because the keel and pylon are an integrated unit, an inventory that could allow for the naturally occurring variety of needed keel sizes and pylon lengths would require an extremely large assortment of integrated keel/pylon units.
It would be advantageous to provide an improved method and prosthesis therefor that avoids the problems associated with the prior art. It would further be advantageous to provide a lightweight modular prosthesis and a method of assembly therefor that can be assembled in a single sequence of steps, maximizing simplicity and minimizing the time expended by the wearer in achieving an acceptable fit.
The difficulties associated with the prior art are overcome by providing an improved prosthetic component and method for assembly wherein the prosthesis comprises prefabricated modular components including a socket adapter, shank or pylon, a keel, and a foot. The method for preparation of the improved prosthesis reduces the time required for prosthesis preparation over that of the prior art, and includes the steps of making a cast of the remaining leg stump and forming a socket therefor; placing the socket in an alignment jig; selecting and assembling a prefabricated keel, pylon, and socket adapter; shaping the socket adapter to a desired configuration; attaching the socket adapter to the socket; draping a final coating of copolymer on the interior pieces, and removing the pylon and socket adapter. There is a single method of adjustment of the prosthesis, which is accomplished by presetting the position of the foot prior to attaching the socket adapter/pylon/keel to the socket. The connecting face of the socket adapter is shaped to incorporate the proper alignment between the socket and the keel, and the length of the pylon is selected to provide the proper length of the prosthesis. The approximate fabrication time for this method is less than one hour, which is a substantial time savings per unit. Because of the reduced preparation time, should the prosthesis prove unsatisfactory, which is common in prosthesis manufacturing, making another prosthesis results in much less wasted man hours.
A solid cast of the residual stump is made in a standard method. When making this cast, a hollow tube or pipe is put in the cast, which provides a basis for vacuum forming a polymer socket over the cast. The socket is allowed to cool and harden, and the plaster is removed. After this, another pipe is held in a correct position in the socket, and a new cast is poured using the socket as a mold.
The socket is supported by the pipe and set up in a support jig until proper orientation is achieved. This can be achieved by aligning and bending the metal pipe to a proper orientation. After this, the appropriate keel, pylon, and socket adapter are selected and assembled under the properly oriented socket. The components are glued to each other, and the assembled keel/pylon/socket adapter is then placed in the correct orientation to the socket and bonded to the socket using rigid foam.
The unit is then removed from the alignment jig, and a majority of the socket is cut away from the cast. The cast then receives any desired modifications. The final coating of copolymer is then applied to the unit, shaped, and allowed to cool and harden. After this step, the pylon, socket adapter, and socket are removed from the shell, and the socket is then returned to the shell and secured. The foot is then glued to the keel.